Discovery of a polymer resistant to bacterial biofilm, swarming, and encrustation

Innovative approaches to prevent catheter-associated urinary tract infections (CAUTIs) are urgently required. Here, we describe the discovery of an acrylate copolymer capable of resisting single- and multispecies bacterial biofilm formation, swarming, encrustation, and host protein deposition, which are major challenges associated with preventing CAUTIs. After screening ~400 acrylate polymers, poly(tert-butyl cyclohexyl acrylate) was selected for its biofilm- and encrustation-resistant properties. When combined with the swarming inhibitory poly(2-hydroxy-3-phenoxypropyl acrylate), the copolymer retained the bioinstructive properties of the respective homopolymers when challenged with Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. Urinary tract catheterization causes the release of host proteins that are exploited by pathogens to colonize catheters. After preconditioning the copolymer with urine collected from patients before and after catheterization, reduced host fibrinogen deposition was observed, and resistance to diverse uropathogens was maintained. These data highlight the potential of the copolymer as a urinary catheter coating for preventing CAUTIs.

For each sample, the centre of the associated square is colored according to the mean value (n=3), whilst the left and right portions are respectively colored ± standard deviation. 1 1 The 8 low attachment monomers produced low attachment copolymers when mixed with similarly low attachment monomers (TMPTA and DMAPA). A few monomers acted synergistically such that copolymers of TMPTA with either EHA, HEA or HDFDA exhibited high attachment whilst the homopolymers remained low attachment. Bacterial biofilm formation generally reduced on copolymers of medium and high attachment controls when mixed with low attachment test monomers TMPTA and DMAPA. OFPMA was particularly susceptible to reduced bacterial attachment, with low bacterial attachment observed on the copolymer containing 30 % (v/v) of TMPTA, whilst medium to high attachment was observed on all copolymers with monomers containing long chain glycols (PPGA and PEGPHEA) up to 50% (v/v). Copolymerisation with the medium attachment test monomers produced similar results across all hit monomers with the exception of EGPEMA, which produced copolymers with medium to high attachment, observed after addition of only 10% (v/v) of the test monomer. Addition of the hit monomers with the high attachment test monomers enabled discrimination of the ability of these monomers to maintain low bacterial attachment once diluted. Monomers tBCHA, BAEDA and HDFDA all achieved low to medium bacterial attachment when copolymerised with either HPHOPA or CMAOE up to addition of 40% of the test monomer and were thus the monomers of choice for the creation of a multi-functional copolymer with the desired microbiological properties.   Thus, the top surface of most of the polymers was contaminated with a thin layer of PDMS oligomers. Different biological behaviours were observed on materials that both contain this contaminant suggesting that either the contaminant is not sufficient to overwhelm the underlying coating chemistry or that the oligomers were washed away in the growth medium during incubation and thus did not impact on the biological performance. Chlorine contamination was also observed on some samples, notably GDGDA, BPAPGDA, pPEGPhEA, PhMA, and tBCHA (Table S3). This group of polymers includes materials that both supported and resisted swarming, suggesting that the biological performance of a material had not been compromised.
The high intensity ions observed for each material (Table S3) were consistent with the chemical structures of the materials synthesised. For example, ions associated with benzyl rings, including C6H5O -, C6H5 + , C7H5and C6H11 + , were observed for materials BPAPGDA, HPhOPA, PhMA, pEGPhEA, PhoPDA, DMDA and tCdMdA, all of which contained benzyl rings or cyclic structures. Unsurprisingly, the ions CF + and Cwere intense for the polymer of TDFHNA, which contains fluorocarbon moieties.
The tBCHA:HPHoPA 2.4:1 copolymer had a high intensity of ions associated with the acrylate backbone (C3H3O2and C2HO -), the benzyl group on HPhOPA (C6H5O -, C6H5O4 + ) and the tert-butyl group of tBCHA (C4H9O + , C4H9 + , C4H7 + ) confirming that both monomers were present at the surface of the copolymer coating. The distribution of the ions appeared to be uniform over the polymer surface ( Fig. S4M-N), suggesting that no micron-scale phase separation of the two monomers had occurred.

Partial least square (PLS) regression model to predict the ability of a polymer to inhibit swarming from molecular descriptors
In the PLS model each of the 4 polymers that resisted swarming had a predicted swarming value greater than 0.4 whilst all of the remaining materials had a predicted swarming value below 0.4, thus, using 0.4 as a threshold value allowed for each of the 11 materials to be correctly assigned as being able to either inhibit or support swarming (Fig. S6B) (32,45). Each of the molecular descriptors was assigned a regression coefficient from which the influence of a particular descriptor on the ability of a polymer to prevent swarming can be determined by assessing the polarity and magnitude (Fig. S6C). Molecular descriptors associated with molecular rigidity, such as the rotatable bond fraction (RBF) and the 3D Petitjean shape index (PJI3), as well as descriptors associated with hydrophilicity, such as the number of hydroxyl groups (nROH), the number of aliphatic tertiary C(sp2) (nR=Ct) and the number of terminal primary C(sp3) (nCp), were included in the model (Fig. S6D). This suggests that for the 11 polymers studied an interplay of molecular rigidity and hydrophilicity influence the ability of a polymer to inhibit swarming. This is similar to the  parameter that correlated with the ability of polyacrylates with aliphatic carbon pendant groups to prevent bacterial attachment (23). This parameter was derived from the combination of the calculated partition coefficient and the number of rotatable bonds. In the present PLS model the hydrophilicity component is more complicated than for the  parameter, whereby an interplay of both hydrophilic groups (nOH) and hydrophobic groups (nR=Ct and nCP) were required to successfully predict whether a material inhibits swarming.         Videos S1 and S2.
DIC videos of the migrating front of P. mirabilis 1885 swarming on a coating of tBCHA (video S1) or HPhOPA (video S2) showing the elongation and alignment of cells at the moving front on tBCHA and the absence of this cell organisation on HPhOPA.